The present invention generally relates to a moving apparatus for driving an optical system in a duplicating machine with the aid of a linear motor.
Recent duplicating machines often move the optical system, instead of moving a document platform, so as to scan the images on a document. A mechanical transmission gear such as wire, pulley or the like is required to convert the revolving power of the motor into rectilinear movements for transmitting the power into an optical system when such optical system movement is effected by the use of a rotary motor. However, it is difficult for a transmission apparatus such as wire, pulley or the like to move the optical system with high accuracy and speed, because an elastic member is used.
An optical moving apparatus for a duplicating machine using a linear motor, which does not require such a transmission apparatus as described, is known.
As disclosed in Japanese Patent Publication (unexamined) Tokkaisho No. 60-136731 there is provided as an arrangement for using a linear pulse motor (LPM) in a linear motor. A stator with uneven-shaped teeth being provided on the top face of a long yoke plate is mounted on the side of the main body of a duplicating machine along the moving direction, so that a rotor supporting an optical system is shaped to linearly move on it. The rotor has a coil-wound -shaped yoke mounted on both the NS polarity ends of a permanent magnet, and has the uneven-shaped teeth on both magnetic poles of each yoke, with the teeth being disposed opposite to the teeth on the side of the stator. Accordingly, a pulse current properly flows to each coil to sequentially generate such magnetic force as absorb the forward teeth on the side of the stator for driving the rotor.
Also, an invention disclosed in Japanese Patent Publication (unexamined) Tokkaisho No. 56-87065 is provided as an arrangement for using a voice coil motor (VCM) in a linear motor. A stator has a long yoke rod mounted on the main body of the duplicating machine along the moving direction, with a long permanent magnet being mounted sideways of the yoke rod, so that a rotor for supporting the optical system is engaged into the yoke rod to be linearly slid. The rotor is provided with a coil slidably wound with respect to the yoke rod. A current for flowing in the coil of the rotor and a magnetic flux in the direction always normal to the moving direction of the rotor are adapted to be formed by the permanent magnet on the side of the stator. Accordingly, a DC current is flowed into the coil, so that the rotor is driven through an electromagnetic force received.
It is necessary for an optical system of a duplicating machine to keep the optical distance constant from the document surface to the exposure position of an exposure member regardless of the scanning position. Thus, the optical system is adapted to move a first mirror platform, which reflects the light from the document surface into the horizontal direction, together with a light source at a scanning speed, and to move a second mirror platform, which reverses the direction of the reflected light by the first mirror platform in the same direction at half of the scanning speed.
A conventional optical system moving apparatus is driven with a linear motor provided on the first mirror platform only. The second mirror platform is moved at half of the scanning speed upon coupling to the first mirror platform through a mechanical coupling apparatus such as a moving pulley or the like. Therefore, conventionally, the linear motor does not drive the optical system at its center of gravity, so that stable movement is not achieved.
When a linear pulse motor is used for the linear motor, a permanent magnet and a coil-wound yoke are placed on a rotor for supporting the optical system, thus resulting in heavier weight on the side of the rotor. The linear pulse motor becomes larger in coil inductance, because the coil is wound around the yoke. Besides, the linear pulse motor is larger in thrust ripple. In this case, the response speed becomes lower, which results in a problem that the moving controlling of higher speed and accuracy is hard to achieve.
When a voice coil motor is used for the linear motor, the magnetic flux to be formed in the entire sliding portion of the rotor is concentrated on both end portions of the yoke rod, so that it is necessary to the sectional area of the end yoke for forming a magnetic path larger. As the permanent magnets on the side of the stator magnetically attract the opposite yoke rods or the like in the entire long portions, the mechanical strength of the entire stator is required to be increased. With the above described structure, it is difficult to make the liner motor lighter in weight.